For the past 6 months I have been speaking and working in French, all day every day. Recently I noticed that I have been forgetting my English — a language that I have spoken my entire life. Can devoting more time to speaking a new language influence your proficiency in your mother tongue?
In regards to bilingualism, linguists identify a native language as L1 and a second learned language as L2. The idea of forgetting or hesitating with your first language is known as L1 attrition or first language attrition. The strength or loss of a language is dependant on the age of language acquisition and language dominance (which language you use more of). The key is the critical period for language development — between 5 years old until around the age of 12 years old. For example, if you speak in your first-language of Italian until you are 5 years old, but then stop and fully switch to English, you will most likely lose your knowledge of Italian, as you are learning English during the critical period for language development.
Although, if you learn another language (L2), but are still dominant in your first language, L1 attrition will be less severe than the previous example (Weinreich, 1963).
A study analyzing the L1 attrition and lexical accessibility of German-Canadians, found that L1 language infrequency was the main contributor to language loss. Therefore the German-Canadians who do not use their native German often, had trouble switching between English (their L2) to their native language, and they had a slower and less-fluent response to naming tasks. As well, these participants had increased hesitation when responding to questions, and “decreased lexical richness in free-speech (de Bot & Clyne in Schmid, 2007).
I believe that the key difference is exposure of a language versus proficiency in a language. For example, I am proficient in French, but most of my life I have been exposed to English. While despite feeling like I am losing my English language while being immersed in a French environment, I still am able to speak English…it just may take more time to switch between languages. This is called temporary language attrition, because French words are coming more quickly to me than English. Although if I end up working in a fully English environment eventually, I will regain my English language fluency.
The moral of the story is: use it or lose it.
Schmid, M. 2007: The role of L1 use for L1 attrition. University of Essex: https://www.researchgate.net/publication/266270687_The_role_of_L1_use_for_L1_attrition.
Weinreich, U. 1963: Languages in contact. The Hague: Mouton.